Many municipal utility systems supply potable water to residents and business in the community for drinking, bathing, manufacturing, and the like. The potable water travels from a treatment plant through pipes known as water mains and branches to the homes and businesses. Water treatment facilities process water from rivers, lakes, and underground in order to supply potable water to the municipal water system. The processing at the treatment facility involves filtering the water to remove particles and microorganisms, adding chemicals to purify the water, and monitoring the quality of the water placed in the water distribution system. After use, waste water generally travels to a waste treatment facility through sewer pipes. The waste water is typically treated to remove wastes and to neutralize fluid contaminants before the water is discharged into lakes or rivers.
A typical water treatment facility for municipalities draws water from a source of fresh water, such as a river, a lake, or groundwater. The water typically moves through the treatment facility by gravity flow, so the water is first pumped to an elevated chemical treatment basin. One chemical alum forms flocs which are sticky globs of slit, bacteria, and other small particles. The water enters a settlement basin where the flocs settle to the bottom for collection. The water is then piped to a filter basin which typically has a layer of sand and gravel. Some filters may include a layer of activated charcoal. The filter collects the larger particles from the water. A reservoir holds the filtered water which receives a final chemical treatment before entering the distribution mains and branches.
Typically, the treatment facility has many settlement filter basins. Inlet manifolds distribute the water through separate pipes into the respective basin. Similarly, outlet manifolds collect the water from the respective basin for communicating the water to the next treatment basin.
The quality of the potable water provided to a municipal water system is carefully monitored. Quality concerns particularly include turbidity, microorganisms, and taste. Turbidity of the water involves the cloudiness caused by particles such as silt and microorganisms. Microorganisms can also cause illness to persons using the water. Disinfection with chemicals kills bacteria. Other processes, such as aeration, improve the taste and odor of the water.
Federal and state environmental legislation directs appropriate government agencies to establish and monitor water quality standards. These agencies set forth the criteria that water systems must meet to maintain government funding and to avoid fines for failing to meet the criteria. One measure of quality is the number and size of particles in the water. One test that water systems must report is the percentage of particles removed during filtration. Various devices have been developed to measure and report information about the number and size of particles in water. One of the devices receives and evaluates a sample of tile water entering the filter basin. Typically the sample is taken from the flow in the discharge pipe at the settlement basin. Another device receives and evaluates a sample of the water discharged from the filter basin. The results are compared to determine the percentage of particulate removed by the filter.
Typically, the particle measuring devices pass the sample of water through a narrow restriction. A supply tube first communicates water to the measuring device from a source such as the discharge pipe of the settlement or filter basin. Typically, a beam of light, such as a laser, is directed into the restriction. Particles in the sample flow deflect light energy from the laser source to a photosensitive device. The device evaluates the reflected light to determine size and concentrations of particles in the water. A microprocessor operatively connected with the measuring device records the concentrations and other relevant data about the nests. The test results can then be reported to appropriate personnel and monitoring agencies. Also, the municipal water company can use the test data to monitor and correct filtration problems.
Known devices measure the sample as a continuous flow and evaluate the flow over a brief period such a one minute. To determine the concentration of particles in the sample, the device must determine the volume in the sample. One device includes a turbine flow meter which determines the volume of water included in the sample being measured. This type of equipment however is expensive and complicated to maintain in the industrial environment of a water treatment facility.
Another known device evaluates water supplied at a constant flow rate. Typically, the water travels at 100 milliliters per minute for particle concentrations of less than 3,000 counts per minute. Heavier concentrations are more readily counted at a slower rate, for example, 50 milliliters per minute.
While the device using a constant flow rate is less expensive and meets the need for monitoring particulate matter in water, drawbacks limit its use. The significant problem is assuring that the proper flow rate of fluid is passing through the measuring chamber during the test. Errors in particle concentration can be made, if the flow rate actually is different from the expected flow rate. For example, a flow rate of 90 milliliters per minute will result in about a 10% error if the device computes particulate concentration based on a flow rate of 100 milliliters per minute. Flow rate can decrease as the pressure of the water being tested decreases. For devices attached to the outlet of the filter, the pressure can decrease over time. As the filter removes particles from the water, the back pressure of the filter increases. The filter becomes a load on the flow of the water through the filter.
An adjustable valve in the discharge tube of the measuring device compensates for the decrease in pressure of the sample fluid entering the measuring chamber. One such valve is an electronic flow controller. This device has a sensor such as a turbine wheel that determines the flow rate of the fluid. The sensor is operatively coupled to a servo valve which opens and closes in response to changes in the flow rate of the fluid entering the measuring chamber. A decrease in the pressure decreases the flow rate of the fluid. The servo valve then opens to allow greater flow through the discharge tube. Opening the discharge tube increases the flow rate of the fluid at the lower pressure so that the measuring chamber receives the expected flow rate of fluid.
Another device is a rotameter placed in-line with the discharge tubing from the measuring chamber to control the flow rate through the chamber. Typically, the rotameter is manually set for the desired flow rate. A float disk controls fluid flow through the rotameter and indicates the flow rate. When the pressure drops as discussed above, the flow rate decreases and the float disk in the valve lowers. The float disk can then be manually reset by turning a needle valve to re-establish the expected flow rate in the measuring chamber. The manually reset rotameter however requires a technician verify and adjust the meter each time the measuring device is to test a sample. Many treatment facilities would require a number of the measuring devices (two for each filter basin) that test samples once or twice per hour. A full-time technician may be required to conduct the tests.
Accordingly, there is a need in the art for an improved fluid flow controller and method for supplying a sample of a fluid to a restriction at a constant rate independent of the pressure of the fluid from which the sample is taken.